Filed on even date herewith are applications of Charles, Jones, Staples, and Wiegner entitled AUTOMATED MICROBIAL ANALYZER and MACHINE AND PROCESS FOR READING CARDS CONTAINING MEDICAL SPECIMENS which describe mechanism and apparatus suitable for analyzing specimens for specific microorganisms using a plastic tray or card which contains a series of dried culture media contained in separate but connected cells, each of the media being specific to a single organism. When the sample is inserted into the card, mixed with the media in the cells, and incubated in the machine, the organism (or organisms) present in the specimen interacts with the culture medium specific to that organism and produces a change in the medium which is read by the machine to indicate the presence of that organism. The change in the medium involves a change in the light transmitting properties of the medium, i.e., a color change or change in turbidity. The change may be caused by metabolic activity of the organism, which, for example, may cause production of acid and a change in pH which causes a color change in a pH sensitive indicator in the medium. The change in the light transmitting properties of the medium also could be caused by a precipitate forming in the medium due to metabolic activity of the organism or it could be caused by growth of the organism.
The specific media designed for use in the aforesaid cards are all designed to favor growth of one microorganism and to inhibit growth of other organisms, are capable of being freeze dried, and can function in the low 0.sub.2 environment of the wells of the card described in detail in said copending applications AUTOMATED MICROBIAL ANALYZER and MACHINE AND PROCESS FOR READING CARDS CONTAINING MEDICAL SPECIMENS.
In media for detection of E. coli, yeast and fungi, and for enumeration, the presence of each of these microorganisms is detected by metabolic activity of the organism which causes production of acid and a change in pH. Accordingly, it is an object of this invention that the pH indicator incorporated into the medium change color at the slightest change toward an acid pH so that the light transmitting properties of medium will change rapidly, thus allowing rapid detection of the microorganism sought to be identified by the mechanism in application AUTOMATED MICROBIAL ANALYZER.
In copending applications filed on even date herewith of Lanham, Rogers, and Meyer entitled E. COLI DETECTION BROTH FOR CLINICAL USE WITH AUTOMATED MICROBIAL ANALYZER; of Lanham, Wilkinson, and Dagy entitled BROTH FOR DETECTING E. COLI IN MIXED WATER SAMPLES; of Lanham, Wilkinson, and Woods entitled E. COLI IDENTIFICATION BROTH; of Meyer entitled ENUMERATION BROTH; and of Gibson and Meyer entitled BROTH FOR INDICATING PRESENCE OF CANDIDA YEAST AND OTHER FUNGI are disclosed media which utilize the reduced aniline blue of this application.
We have discovered a method of reducing the dye aniline blue so that it will change color toward acid pH, thus changing the light transmitting properties of any medium into which it is incorporated. The change in pH to which we are referring is caused by production of acid. The color of the reduced aniline blue is tan or colorless at a pH of 7.0. Upon production of acid by unknown microorganisms, the reduced aniline blue will change to blue. This change will take place within 12 to 18 hours, thus allowing rapid detection of microorganisms in clinical specimens by the mechanism of application AUTOMATED MICROBIAL ANALYZER which detects blue.
The reducing agent of the present invention is sodium thioglycollate. This reducing agent is useful in this invention because it will not inhibit growth of microorganisms, as do otherwise suitable chemical reducing agents.